This application claims the benefit of Korean Application No. 99-37905, filed Sep. 7, 1999, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus and method for detecting the rate of rotation of a motor, and more particularly, to an apparatus and method for detecting the rate of rotation of a DC spindle motor without using an additional frequency generation (FG) signal generator in electronic equipment using the DC spindle motor.
2. Description of the Related Art
Electronic equipment such as DVDPs, CDPs and VCRs employing a spindle motor generally use a brushless motor. FIG. 1 shows the configuration of a general disk drive. In a disk driver employing a constant linear velocity (CLV) recording method, the rate of rotation of a disk continuously varies from about 500 rpm (at the innermost circumference) to about 200 rpm (at the outermost circumference) according to the reproduction position of a pickup.
Referring to FIG. 1, a CLV servo block 104 applies a voltage for rotating a disk 101 at a preset initial speed to a spindle motor 102 via a driver 103. Thus, the disk 101 begins to rotate, and information recorded on the disk 101 is converted into an analog radio frequency (RF) signal by a pickup 105. The converted analog RF signal is output to a signal processing block 106. Then, the signal processing block 106 converts the analog RF signal into a pulse waveform and outputs the pulse waveform to the CLV servo block 104.
In the CLV servo block 104, a digital phase-locked loop (PLL) circuit generates a bit clock which is synchronized with a reproduction signal. Thereafter, the bit clock is compared with a system clock in an automatic frequency control (AFC) detection circuit and a phase comparing circuit to output a control voltage to the driver 103. In other words, when a bit clock frequency is lower than a system clock frequency, the voltage applied to the spindle motor 102 is increased to increase the rate of rotation. On the other hand, when the bit clock frequency is higher than the system clock frequency, the voltage is decreased to decrease the rate of rotation.
When the bit clock frequency is equal to the system clock frequency through such control, the disk reproduction speed becomes equal to a linear velocity for recording, so that the data on the disk can be reproduced within a range of the linear velocity adapted for recording.
A tracking and focusing (T/F) servo block 107 is for servo tracking and focusing. In other words, the T/F servo block 107 creates en electrical signal corresponding to a beam tracing state and moves an object lens and a body of the pickup 105 in a radial direction of the disk 101 based on the created electrical signal, thereby carrying out the servo tracking for controlling a beam to trace a track. In addition, the T/F servo block 107 employs an astigmatism method and a critical angle detecting method to carry out the focusing servo for controlling the pickup 105 such that the object lens is focused on the reflective surface of the disk 101.
When switching from one surface of the disk 101 to the other surface of the disk 101 during reproduction (such as the pickup 105 moving to the other side of the disk 101), a voltage for accelerating the disk 101 in a direction of reproduction is applied to the spindle motor 102 until the pickup 105 moves to a target position for reproduction, and then CLV servo is carried out to control the driver 103 such that the disk 101 rotates at a constant velocity.
However, when it takes long for the pickup 105 to reach the target position, the rate of rotation of the spindle motor 102 continuously increases, and consequently, an accelerated mode in which the rate of rotation exceeds a prescribed rate of rotation occurs. A controller 108 detects the rate of rotation of the spindle motor 102 and determines the accelerated mode when a speed exceeding the prescribed speed is detected. If the accelerated mode is determined, the controller 108 applies a command for stopping reproduction to the CLV servo block 104 to protect the system. In addition, the controller 108 detects the rate of rotation of the spindle motor 102 to control the spindle motor 102 depending on the mode.
Accordingly, conventional technologies employ a brushless motor as the spindle motor 102 and generate a frequency generation (FG) signal proportional to the rate of rotation of the spindle motor using an FG signal generator, as shown in FIG. 2. In other words, a signal detected by a Hall device 201 within the brushless motor is converted into a pulse signal by a comparator 202 to generate an FG signal which is output to the controller 108.
This brushless motor is more expensive than a DC motor and the manufacturing process thereof is poor. When employing a DC motor as a spindle motor according to conventional technologies, since the DC motor does not have a Hall device, it cannot generate an FG signal for detecting the rate of rotation. Consequently, an additional FG signal generator must be employed. In this case, the costs increase and the manufacturing process is also poor due to the addition of an apparatus.
To solve the above problems, it is an object of the present invention to provide an apparatus and method for detecting the rate of rotation of a DC spindle motor without using an additional frequency generation (FG) signal generator while employing a DC motor as the spindle motor for a disk drive.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and other objects of the present invention, there is provided an apparatus for detecting a rate of rotation of a DC spindle motor. The apparatus includes a current-to-voltage converter which detects and converts a current proportional to a magnitude of a current supplied to the DC spindle motor into an analog voltage, an analog-to-digital converter which converts the analog voltage output from the current-to-voltage converter into a digital signal, and a controller which detects the rate of rotation of the DC spindle motor using the digital signal output from the analog-to-digital converter and controlling the DC spindle motor in accordance with the detected rate of rotation.
In another aspect, there is provided a method of detecting a rate of rotation of a DC spindle motor. The method includes: (a) detecting a current supplied to the DC spindle motor; (b) generating a digital signal proportional to the magnitude of current detected in the step (a); and (c) determining the rate of rotation of the DC spindle motor based on the digital signal and controlling the DC spindle motor according to the determined rate of rotation.
The step (b) includes: (b1) converting the current detected in the step (a) into an analog voltage; and (b2) converting the analog voltage obtained in the step (b1) into the digital signal.